Boreholes are drilled thousands of feet underground for oil, gas, and other purposes. Drilling is accomplished by utilizing a series of connected pipes called a drill string. At the bottom of the string is a drill bit. The drill bit turns either by rotating the drill string or by a fluid, typically referred to as “drilling mud” that travels through an internal passage in the drill string. The drilling mud powers a motor near drill bit. The drill bit advances into the earth, thereby forming the borehole. A high pressure fluid, the drilling mud, is pumped down through internal passage of the drill string to the drill bit so as to lubricate the drill bit and to flush cuttings from its path. The drilling fluid F then flows to the surface through an annular passage formed between the drill string and the surface of the bore hole.
Data regarding the downhole drilling operation and environment is often transmitted from sensors located near the drill bit to the surface while the borehole is being drilled. Obtaining and transmitting drilling data between sensors located downhole and the surface is commonly referred to as measurement-while-drilling (MWD) and logging-while-drilling (LWD), which are collectively referred to as MWD throughout this document. Often, a transmitter and sensor package is part of an MWD tool. Typical data includes formation characteristics, borehole direction and inclination, and various other drilling parameters.
MWD tools can be a fixed-mount tools that are permanently fixed to the drill collar, or retrievable tools configured so that all or part of the MWD tool can be retrieved from the drill collar as needed. A fixed mount tool has some advantages, but a drawback is that if the drill string becomes permanently stuck, the expensive MWD tool is also stuck. A retrievable tool, in contrast, can be pulled out of the drill string even if the drill string is permanently stuck and lost. Retrievable tools typically include a probe, sometimes called a stinger, that seats in a mule shoe mounted inside a section of drill collar located toward the drill bit. The mule shoe includes a socket into which the probe inserted. In conventional retrievable tools, grooves align the probe in the socket of the mule shoe to orient the probe. In the event the drill string gets stuck, a wireline is used to lower a device which can attach to a spear point mounted on the uphole end of the retrievable MWD tool. When the wireline is attached to the retrievable MWD tool, the tool can be pulled up to the surface through the internal passage of the drill string.
Drilling can cause the drill bit to move up and down violently against the earthen formation. In order for accurate information to be provided by the MWD tool, the probe should be seated properly and securely in the mule shoe. If the probe is not properly seated, the sensors might make erroneous measurements due to the axial movement of the drill bit. For example, if the probe is not seated properly in the mule shoe, a directional sensor in the MWD tool may be come misaligned with axis of the drill string and the formation, and in this way provide incorrect information, which can result in steering the borehole in a wrong direction. Some minor up and down movement of the probe is acceptable during drilling. However, even in vertical boreholes where the weight of the MWD tool tends to keep the probe in place, some means for holding the tool in place relative to the socket is desirable to minimize axial vibration which can result in inaccurate measurements, damage to sensors, and premature wear and failure. While the probe should be properly seated in the mule shoe across a range of operating conditions downhole, it should also be easy to release the probe when necessary for retrieval.
Previous designs have utilized latching mechanisms to overcome the issue of keeping downhole equipment securely in place. See for example, U.S. Pat. No. 6,896,050, assigned to the APS Technology, Inc. However, latches have reliability concerns because they can be made of small moving parts exposed to fast flowing, abrasive drilling fluid F. In addition, the shock forces can be large, and latch mechanisms are subject to breaking. Accordingly, there is opportunity for improvement in the art.